182 
NATJTILOIDEA. 
ISTot considering this a satisfactory way of settling the difficulty, 
I communicated with Dr. Lindstrom, who wrote to me (June, 1887) 
as follows : — “ I have had the type specimen of Barrande’s 
0. imbricatum as a loan from Prague, and it is as faithfully figured 
in his grand work as all his specimens prove to be. I have, how- 
ever, strangely enough, not found a single Gotland Orthoceratite 
which I may pronounce as identical with that type. I see no other 
way but to drop 0. Wahlenberg, and keep 0. imbricatum^ 
Hisinger, for that long so- named, as I have proposed long ago . . . . ” 
Dr. Lindstrom adds, “la fortnight ago inspected an old col- 
lection kept in Upsala, named the Marklinian Collection, a gift to 
the University by [Marklin] an old collector and contemporary of 
Wahlenberg. There I found both 0. imbricatum and angulatum^ 
with specimens quite such as we have always been wont to name 
with those names.” 
As Wahlenberg’s description of his species was very brief and un- 
accompanied with figures, and as no specimens answering to his 
definition of it can now he found in any of the Swedish Collections, 
I think that the course suggested by Dr. Lindstrom is the most con- 
venient under the circumstances, and accordingly I have adopted it. 
It will now he unnecessary for me to make any further mention 
of OrtJioceras Marloense Phillips (ante^ p. 19), further than to say 
that I of course cannot accept Prof. Blake’s view that it is identical 
with the imbricatum of Hisinger. Prof. Blake does not appear to 
have examined any actual specimens of Actinoceras imbricatum^ or 
he could not have failed to note that the siphuncle, instead of being 
“ very fine and filiform,” is large and nummuloidal, and could there- 
fore have no affinity with any such species as he describes under 
Wahlenherg’s name. 
Horizon. Upper Ludlow. 
Locality. Island of Gothland, Sweden. 
Well represented in the Collection. Two of the specimens were 
presented by A. H. Poord. 
Actinoceras Backi, Stokes. 
1824. Orthocerce . . . ., Bigshy, Trans. Geol. Soc. vol. i. pt. 2, p. 204, 
pi. XXX. f. 1. 
1840. Ormoceras Bachi, Stokes, Trans. Geol. Soc. vol. v. pt. 3, p. 709 ; 
with a reference to Bigshy’ s figures (loc. cit.). 
1857. Orthoceras rotulatum, Billings, Geol. Surv. of Canada, Report of 
Progress for the years 1853-1866, p. 334. 
1870. Orthoceras rotulatum, Barrande, Syst. Sil. de la Boheme, vol. ii. 
Texte iii. 1874, p. 732, pi. ccccxxxvii. ff. 1-5. 
